Amplifier fault

[sleah]

I have a quite old, but rather nice (IMHO) Ramsa 400x400 MOSFET power amp that is retired from gigging but I have setup at home.

 

Recently, on switching on, the RH channel has taken to making lots of loud(ish) crackling noises. Unaffected by connections (apart from the fact the noise is coming from the speaker....) or position of the attenuator. It is definitely the amp and not the speaker.

After 5-10 minutes the cracking will stop. While it is crackling the channel otherwise works normally, so with loud music it will partly drown out the crackles!

 

I've tried waggling internal connections, cleaning plugs etc and tapping the PCB to no avail.

As it stops after a while - only to return when powering up again a day or so later - it must be temperature related to some extent.

 

Is it likely to be capacitors? Does it need a recap? I think it's unlikely the PSU as (I'd need to double check in case I'm losing it..) it is a single PSU shared by both channels - Huge TX and huge caps :D

 

Any thoughts gratefully received.

[stagemanagement]

The last time I heard loud crackling noises from an amp, it was the capacitors - they were alight and flames were licking out of the air vents!!

 

Change it now, it's not pretty if it bursts all over the inside of the unit...

[alistermorton]

The other thing that occurs to me is a slight dry joint that is moving as the unit heats up. Have you tried reflowing all the connections?

[jamesperrett]

I'd say it is more likely to be a transistor as they're more likely to warm up after a while. It probably needs the use of an oscilloscope to trace where the noise is coming from.